The present invention relates to a method for inductively heating a substrate and a coating on the substrate.
The present method overcomes problems that can arise when attempting to heat substrates having coatings, particularly relatively thick and poorly heat conductive, for example plastic coatings. For example, while it is known to employ induction heating to heat polyolefin coated pipe, difficulties can arise when the coating is relatively thick. For example, in the case of applying a covering to a weld joint in polypropylene coated pipe, with certain covering systems, it is desired to raise the temperature of the metal at the cutback portion to a minimum of 165° C., preferably about 180° C. and the exterior of the polypropylene covering to a minimum of about 145° C., but more preferably about 165° C. Where the coating is greater than about 3 mm thick, for example 6.0 mm thick or greater, it has been found that induction heating is incapable of raising the exterior surface of the polypropylene coating to the desired temperature without prolonged and intensive induction heating that tends to excessively heat the steel substrate with the result that the coating components degrade, deform and decompose.